1. Field of the Invention
The present invention relates to a LED (light-emitting diode) exposure head with overlapping electronic circuits for use in a recording apparatus for linewise recording information on a moving photoreceptor.
2. Description of the Prior Art
A LED exposure head is known that comprises an assembly in alignment of a plurality of LED modules mounted on a common base, and an elongated lens array parallel to the row of LED's. The head is mounted in a housing allowing the mounting of the head in the recording apparatus and also offering protection of the optical and electronic components against environmental conditions.
Each LED module of the head is in fact an assembly of the following on a tiny metal base plate, which functions as a mounting tile.
A row of LED dice with LED's, which lie along the center of the assembly, and are cemented to the front face of the base plate.
On each side of the row of LED dice on each base plate there is a row of several integrated circuit chips which are likewise cemented to the base plate. The chips comprise the drivers for the LED's, a shift register, and occasionally other control circuits.
On the outside of the row of integrated circuit chips on each side of the center line, there is a circuit board cemented to each base plate. The circuit board may be in the form of a printed thick film circuit on a ceramic base, and may comprise trimming resistors, blocking capacitors and probe pads for the testing of the modules, prior to their mounting on the common base.
The modules are mounted in closely adjacent relationship on the base of the exposure head which forms a foundation for the head.
The exposure head finally comprises two elongated interconnection circuit strips that extend at either end of the modules over the length of the exposure head, and that are wire bonded to the circuit boards to bring signals and power to the assembly.
A disadvantage of this known exposure head is its relatively large width, resulting from the location of the different components of the modules beside each other, in the transverse direction of the modules. Yet, a reduced width of the exposure head is desirable, in particular in those instances where two or more colour developments must be performed around a semiconductor drum of a recording apparatus. A development station requires quite some angular space around a semiconductor drum and this space is difficult to reduce.
It is easy to obtain a larger angular space for the different components by using a semiconductor drum of a large diameter, but this adds to the expense and the overall size of the recording apparatus.